Convert IST to AST
AST is 9 hours 30 minutes behind IST. IST is UTC+5:30 and AST is UTC−4.
Right now: IST · AST
Which IST is this?
IST names more than one zone. This page reads it as India Standard Time at UTC+5:30, which is the reading most converters take. There are others: Israel Standard Time at UTC+2, used in Israel in winter; Irish Standard Time at UTC+1, used in Ireland in summer.
The letters on a meeting invitation do not say which one is meant. If yours is not India Standard Time, the answer above is wrong, and not by a little:
| If IST means | Then |
|---|---|
| India Standard Time — assumed on this page | AST is 9.5 hours behind IST |
| Israel Standard Time | AST is 6 hours behind IST |
| Irish Standard Time | AST is 5 hours behind IST |
The large converter sites disagree about this as well: search for a IST conversion and some of the results answer for one reading and some for another, none of them saying which they chose. Where it matters, ask which country the sender is in rather than which letters they typed.
Which AST is this?
AST names more than one zone. This page reads it as Atlantic Standard Time at UTC−4, which is the reading most converters take. There is one other: Arabia Standard Time at UTC+3, used in Saudi Arabia, Iraq, Kuwait, Bahrain, Qatar and Yemen.
The letters on a meeting invitation do not say which one is meant. If yours is not Atlantic Standard Time, the answer above is wrong, and not by a little:
| If AST means | Then |
|---|---|
| Atlantic Standard Time — assumed on this page | AST is 9.5 hours behind IST |
| Arabia Standard Time | AST is 2.5 hours behind IST |
The large converter sites disagree about this as well: search for a AST conversion and some of the results answer for one reading and some for another, none of them saying which they chose. Where it matters, ask which country the sender is in rather than which letters they typed.
Best time to schedule a meeting
Standard 9–5 working hours do not overlap at all between IST and AST. Someone has to take an early or late call — or use asynchronous communication instead.
| IST | AST | Suitable? |
|---|---|---|
| 9:00 AM | 11:30 PM (previous day) | outside 9–5 |
| 10:00 AM | 12:30 AM | outside 9–5 |
| 11:00 AM | 1:30 AM | outside 9–5 |
| 12:00 PM | 2:30 AM | outside 9–5 |
| 1:00 PM | 3:30 AM | outside 9–5 |
| 2:00 PM | 4:30 AM | outside 9–5 |
| 3:00 PM | 5:30 AM | outside 9–5 |
| 4:00 PM | 6:30 AM | outside 9–5 |
| 5:00 PM | 7:30 AM | outside 9–5 |
IST to AST conversion table
| IST | AST |
|---|---|
| 12:00 AM | 2:30 PM (previous day) |
| 1:00 AM | 3:30 PM (previous day) |
| 2:00 AM | 4:30 PM (previous day) |
| 3:00 AM | 5:30 PM (previous day) |
| 4:00 AM | 6:30 PM (previous day) |
| 5:00 AM | 7:30 PM (previous day) |
| 6:00 AM | 8:30 PM (previous day) |
| 7:00 AM | 9:30 PM (previous day) |
| 8:00 AM | 10:30 PM (previous day) |
| 9:00 AM | 11:30 PM (previous day) |
| 10:00 AM | 12:30 AM |
| 11:00 AM | 1:30 AM |
| 12:00 PM | 2:30 AM |
| 1:00 PM | 3:30 AM |
| 2:00 PM | 4:30 AM |
| 3:00 PM | 5:30 AM |
| 4:00 PM | 6:30 AM |
| 5:00 PM | 7:30 AM |
| 6:00 PM | 8:30 AM |
| 7:00 PM | 9:30 AM |
| 8:00 PM | 10:30 AM |
| 9:00 PM | 11:30 AM |
| 10:00 PM | 12:30 PM |
| 11:00 PM | 1:30 PM |
About IST
India Standard Time (IST) is UTC+5:30. It is used in all of India and Sri Lanka, on a half-hour offset.
India Standard Time is UTC+5:30 — one of the handful of zones offset by half an hour, which breaks any code that assumes whole-hour offsets and any mental arithmetic that does the same. India has no daylight saving and one time zone for the entire country, despite spanning nearly 30 degrees of longitude. The abbreviation is also used for Irish Standard Time and Israel Standard Time, both of which are entirely different offsets.
About AST
Atlantic Standard Time (AST) is UTC−4. It is used in Halifax, Puerto Rico and the eastern Caribbean in winter.
Atlantic Standard Time is UTC−4, one hour ahead of Eastern. It covers Canada's Atlantic provinces, Puerto Rico and much of the eastern Caribbean, and it is the reason a call from Halifax to Toronto is an hour out from what either party expects. The abbreviation is also used for Arabia Standard Time at UTC+3, seven hours away in the other direction, which is a genuinely dangerous collision in scheduling.
Does this gap change with the seasons?
Neither IST nor AST shifts with the seasons, so this 9.5-hour difference holds all year. That is unusual enough to be worth relying on: most cross-continental gaps move twice a year.
This is the reason scheduling systems store an IANA zone such as Region/City rather than an offset or an abbreviation: the zone knows its own rules and the offset does not.
Frequently asked questions
What time is 9:00 AM IST in AST?
9:00 AM IST is 11:30 PM AST (previous day).
Is AST ahead of IST?
AST is 9 hours 30 minutes behind IST.
Which time zone does this use?
IST is UTC+5:30 and AST is UTC−4. Both abbreviations denote a single fixed offset, so this conversion never shifts with daylight saving — what changes is which abbreviation a place is using at the time.